linux-kernel - Re: [PATCH 01/15] tick/nohz: Remove duplicate between tick_nohz_switch_to_nohz() and tick_setup_sched

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Date: Thu, 25 Jan 2024 14:34:06 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Frederic Weisbecker <frederic@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Peng Liu <liupeng17@...ovo.com>,
 Ingo Molnar <mingo@...nel.org>, Anna-Maria Behnsen
 <anna-maria@...utronix.de>, Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH 01/15] tick/nohz: Remove duplicate between
 tick_nohz_switch_to_nohz() and tick_setup_sched_timer()

On Thu, Jan 25 2024 at 12:57, Frederic Weisbecker wrote:
> On Thu, Jan 25, 2024 at 10:12:20AM +0100, Thomas Gleixner wrote:
>> Adding
>> 
>> #define tick_nohz_highres_handler NULL
>> 
>> for CONFIG_HIGH_RES_TIMERS=n somewhere allows you to write that as:
>> 
>> 	if (IS_ENABLED(CONFIG_HIGH_RES_TIMERS) && mode == NOHZ_MODE_HIGHRES)
>> 		ts->sched_timer.function = tick_nohz_highres_handler;
>
> So the next patch does:
>
> if (mode == NOHZ_MODE_HIGHRES)
>     ts->sched_timer.function = tick_nohz_highres_handler;
>
> Because that condition only happens in CONFIG_HIGH_RES_TIMERS anyway
> and the function field exists in any case.

Right, but the function does not exist for HRES=n, so you need the
#define ... NULL. The IS_ENABLED() allows the compiler to eliminate the
code for HRES=n completely.

Thanks,

        tglx